Interpretive Handbook

Salivary adenoid cystic carcinomas (ACC), although uncommon, are frequent among salivary gland malignancies. ACC is typically an aggressive tumor with a poor prognosis. Histologically, ACC show significant morphologic overlap with other salivary gland tumors, but have a much different clinical course. Because ACC requires a management distinct from histologically similar lesions, it is important to make an accurate diagnosis. Translocations between MYB (6q23.3) and NFIB (9p24) have been identified in a large proportion of primary salivary gland ACC. These alterations have not been identified in other salivary gland tumors. Therefore, separation of MYB, in the proper clinical and histologic context, is diagnostic for ACC and can be confirmed by FISH with MYB break-apart probes.

The presence of MYB rearrangement helps to confirm the diagnosis of adenoid cystic carcinomas (ACC) in the proper histologic context.

The absence of MYB rearrangement does not exclude the diagnosis of ACC, as a subset of ACC do not show a MYB rearrangement.

A positive result is detected when the percent of cells with an abnormality exceeds the normal cutoff for the probe set.

A positive result suggests rearrangement of the MYB locus. The presence of a MYB rearrangement in conjunction with the proper clinical and histologic features, is diagnostic of ACC. A confirmed diagnosis of ACC results in specific clinical management that may be distinct from the management of other salivary gland neoplasms.

A negative result suggests no rearrangement of the MYB gene region at 6q23.3. The absence of a MYB rearrangement does not exclude the diagnosis of ACC, as a subset of ACC do not show a MYB rearrangement.

This test is not approved by the FDA, and it is best used as an adjunct to existing clinical and pathologic information.

This test is only intended to be used in the diagnosis of salivary gland tumors. This test has not been validated on adenoid cystic carcinoma (ACC) arising from nonsalivary gland locations. The results of this test are intended to be interpreted in association with the pathologic and clinical findings. The absence of MYB rearrangement does not exclude the diagnosis of ACC.

Fixatives other than formalin (eg, Prefer, Bouin) may not be successful for FISH assays. Although FISH testing will not be rejected due to nonformalin fixation, results may be compromised.

Paraffin-embedded tissues that have been decalcified are generally unsuccessful for FISH analysis. The pathologist reviewing the hematoxylin and eosin-stained slide may find it necessary to cancel testing.